1. Field of the Invention
In photochemical reactions, the course of the reaction can be affected by the excited state from which the product is formed. The excited state is determined initially by the energy absorbed by the molecule, but the initial state may be changed by interaction with the molecule's environment. Singlet and triplet states are the common photochemical excited states, which may be achieved by either direct absorption of energy, particularly light, or by use of a sensitizer.
The reaction product can depend on the excited state from which the reaction product is derived, not only as to isomer, but also in some cases as to structure, such as cyclizations. Therefore, where the possibility exists for two different products to be obtained, depending on the nature of the excited state, a quencher may be employed to dissipate the energy of one of the excited states in a manner which does not result in product formation.
Quenchers also find use in the study of photochemical reactions. In order to ascertain whether a particular product is formed through a triplet or singlet state, a quencher may be employed which will prevent the reaction from going through a triplet state. In this manner, if the reaction proceeds in the presence of the quencher, assuming the quencher has the appropriate triplet energy value (E.sub.T), then the triplet state of the reactant must be very short lived or the reaction must proceed by means of a singlet state.
The lower the triplet energy value for a molecule which is undergoing reaction, the lower the triplet energy value required for the quencher. Therefore, quenchers with low triplet energy values can be quite valuable in being able to quench reactions which occur at relatively low energy values. However, the quencher must not absorb the exciting light as this would inhibit the photochemical reaction. Ideal quenchers, therefore, have high singlet energies, preferably greater than about 60 kcal/mode, and low triplet energies, preferably less than about 45 kcal/mole.
In addition, numerous degradative reactions of both dyes and polymeric materials are the result of free radical reactions. A free radical is usually formed initially, which can react with oxygen to form a peroxide or hydroperoxide. Breakage of the oxygen-oxygen bond results in the formation of additional radicals which, by abstraction or addition, form new radicals, which then add to oxygen. Since cleavage of the peroxide gives two radicals, the process is autocatalytic. By providing a material which is stable but reactive toward radicals, the chain of peroxide formation can be broken and the life of the host or substrate material greatly extended.
2. Description of the Prior Art
A list of quenchers may be found in the 1971 J. T. Baker catalog. A description of the use of quenchers may be found in Turro, "Molecular Photochemistry", Benjamin, New York, 1967. The reaction of 1,2-bis(hydroxylamino)tetramethylethane is reported to give a 1-oxylaziridine in Luckhurst, et al, Tetrahedron Letters, 1971, 675. Heterocycles having the diazoxy functionality are reported by Snyder, et al, Tetrahedron Letters, 1971, 4693; Tun, et al, Org. Mass. Spect. 3, 1055 (1970) Luttke, et al, Liebigs, Ann. Chem 687, 236 (1965), Beilstein II, Band V. pg. 26 (Piloty, et al, Ber. 35, 1303) particularly 1,4 dibromo, and 1,4 dichloro-2,3-diazabicyclo[2,2,2]oct-2 en-2,3-dioxide and 2,3-diazabicyclo[2,2,1]hept-2-en-2,3-dioxide.